IC-910H Service manual - n7tgb

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While in SSB mode, the amplified signals from the buffer amplifier (Q1651) are then applied to the balanced modulator (IC201). While in AM/FM mode, the amplified signals from the buffer amplifier (Q1651) are applied to the limiter amplifier (IC1651b) and splatter filter (IC1651a). The signals are passed through the buffer amplifier ((IC1652a) and are then applied to the AM detector (IC1807d, D1652) in AM mode or to the varactor diode (D253) in FM mode. 4-2-4 TRANSMIT IF AMPLIFIER CIRCUIT (MAIN UNIT) The modulated IF signal from a modulation circuit is applied to the IF amplifier circuit (Q1). The amplified IF signal is then applied to the VHF/UHF transmit circuit (PA unit) via the VHF /UHF switching circuit (D52, D53). The gain of the IF amplifier circuit (Q1) is controlled by the ALC amplifier circuit (IC1601b). Therefore, the IF amplifier is reduced when the output power increases. 4-2-2 MODULATION CIRCUIT (MAIN UNIT) (1) FM mode The amplified audio signals from IC1701 are pre-emphasized and limited at IC1651b and then passed through the splatter filter (IC1651a). The filtered signals are then applied to the FM modulation circuit (D253) via the FM deviation level controller (IC1803 pins 21, 22) and buffer amplifier (IC1652a). Also, subaudible tone signals from the CPU (DISPLAY board; IC1 pin 4) are applied to the FM modulation circuit (D253) via the splatter filter (IC1651a). The FM modulation circuit changes the generating frequency of the FM local oscillator (Q254, X251) to generate an FM signal. The modulated IF signal is passed through the RF limiter (Q253) and then applied to the transmit IF amplifier circuit. When 9600 bps mode is selected, audio signals from the ACC connector bypass the amplifiers and are applied to IC1654a directly via the external modulation switch (IC1531, pins 12, 1). In such cases, the deviation detector (IC1807d) cuts off the audio line when over modulation is detected. (2) SSB and CW modes The amplified audio signals from Q1651 are mixed with BFO signals at the balanced mixer circuit (IC201) to produce a 10 MHz IF signal. The mixed signal is still a DSB signal, therefore, the mixed signal passes through bandpass filter circuit (FI151) to suppress unwanted side band signals. The filtered signal is applied to the transmit IF amplifier circuit • Transmit IF frequencies Mode USB LSB CW Transmit IF signal 10.8485 MHz 10.8515 MHz 10.8491 MHz 4-2-3 CW KEYING CIRCUIT (MAIN UNIT) When the CW key is closed, control signal is output from CPU (LOGIC unit) and controls break-in operation, the side tone signal. Keying signals (DOT and DASH) from the [KEY] jack (J1401) are applied to the CPU (DISPLAY board; IC1, pins 49, 48 respectively), and the CPU outputs a CW control signal (KDS1) from pin 21. The CW control signal is applied to the balanced mixer (IC201) via Q201, D201, D207 to unbalance the IC201 input bias voltage and creates a carrier signal. R202 determines the transmit delay timing. 4-2-5 RF CIRCUIT (PA UNIT) The RF circuit consists of mixer and drive amplifiers to obtain the desired frequency and level needed at a PA circuit, respectively. (1) VHF band The IF signal from the MAIN unit (P501) is mixed with an LO signal from the VHF VCO circuit (PLL unit; Q191, D191–D194) at the double-balanced mixer circuit (Q501, Q502, D502) to be converted into VHF transmit frequency. The mixed signal is passed through the attenuator (R512–R514) and two-stage tunable bandpass filter (D503, L533 and D504, L504) to suppress spurious components. The filtered signals are then amplified at the YGR amplifier (IC501) and passed through the attenuator (R562–R531) and another two-stage tunable bandpass filter (D641, L641 and D642, L642) The amplified and filtered RF signal is applied to the drive amplifier circuit that is used VHF and UHF signals commonly. (2) UHF band The IF signal from the MAIN unit (P1) is mixed with a 2nd LO signal at the double-balanced mixer circuit (Q1, Q2) to produce a 2nd IF signal (71.25 MHz). The 2nd LO signal (60.4 MHz) is generated at the reference oscillator and doubler circuit (PLL unit; X512, Q551) via LO amplifier (IC40). The 2nd IF signal is amplified at the buffer amplifier (Q3) via the bandpass filter circuit (L3, L4, C12, C13, C15–C17, C24, C26). The amplified 2nd IF signal is applied to the 1st mixer circuit (D190, L190, L191) passing through the attenuator (R12–R14) and low-pass filter (L381, L382, C381–C383). The 1st mixer circuit (D190, L190, L191) converts the 2nd IF signal into a UHF transmit frequency with a 1st LO signal from the UHF VCO circuit (PLL unit; Q391, D391–D394). The converted RF signal is passed through the bandpass filter (FI200 and FI201) where unwanted LO signal emission is reduced. The filtered signal is attenuated at R204–R206 and amplified at the YGR amplifier (IC200), and is then applied to the drive amplifier circuit via the band pass filter (FI202) and another YGR amplifier (Q200). 4-2-6 DRIVE AMPLIFIER CIRCUIT (PA UNIT) The drive amplifier circuit amplifies RF signals from the VHF or UHF RF circuit to obtain a level needed at the power amplifier circuit. One drive amplifier circuit is commonly used for both VHF and UHF band signals. The signals from the VHF or UHF RF circuit are amplified at the drive amplifier circuit (Q101, Q121, Q131, DRV board; Q930). The amplified VHF signals are passed through the 4 - 4
low-pass filter and UHF signal are high-pass filter, and then applied to the VHF and UHF power amplifier circuit separately. 4-2-7 POWER AMPLIFIER CIRCUIT (PA UNIT) The power amplifier circuit amplifies the RF signals to the specified output power. (1) VHF power amplifier circuit The RF signal from the low-pass filter circuit is applied to the VHF power amplifier circuit (Q651, Q652) to obtain a stable 100 W of RF output power. The amplified RF signal is applied to the antenna connector (CHASSIS; J1) via the power detector (D720, D721), transmit/receive switching relay (RL700) and low-pass filter (L723–L721, C728–C726, C728) circuits. (2) UHF power amplifier circuit The RF signal from the high-pass filter is applied to the UHF power amplifier circuit (Q151, Q152) to obtain a stable 75 W of RF output power. The amplified RF signal is applied to the antenna connector (CHASSIS; J2) via the transmit/receive switching circuit (D182–D185), low-pass filter (L181, L180, C188–C184) and power detector (D180, D181) circuits. 4-2-8 ALC CIRCUIT (PA AND MAIN UNITS) The ALC (Automatic Level Control) circuit protects the power amplifiers (PA unit; Q651, Q652 for VHF and Q151, Q152 for UHF) from a mismatched output load. Also, the ALC circuit controls the gain of the transmit IF amplifier in order for the transceiver to output even when the supplied voltage shifts, etc. The RF power level is detected at the power detector circuit (PA unit; D720–D721 for VHF, D180, D181 for UHF) to be converted into DC voltages. The detected voltage (VFOR for VHF or UFOR for UHF) is passed through the switching diode, and are then applied to the differential amplifier (MAIN unit; IC1601b) via the FOR line. A reference voltage (POCV) for IC1601b is controlled by the [RF PWR] control to output reference voltages. The output voltage is applied to the transmit IF amplifier circuit (MAIN unit; Q1) as an ALC signal to control the amplifier gain. When the VFOR/UFOR voltage increased, the output from the differential amplifier will be decrease to reduce the IF amplifier gain. This adjusts the RF output power until the VFOR/UFOR and POCV voltage are well balanced. 4-3 PLL CIRCUITS IC-910H contains 2 PLL circuits and 1 local oscillator. The VHF and UHF PLL circuits adopt “Icom’s original I-loop PLL” to obtain very fast lock up times. 4-3-1 VHF PLL CIRCUIT (PLL UNIT) The VHF PLL circuit generates the 1st LO frequency, and the signal is applied to the VHF 1st mixer circuit in the PA unit as the “A1LO” signal. The PLL circuit consists of a VCO, prescaler and DDS circuits. The signal generated at the VHF VCO circuit (Q191, D191–D194) is amplified at the buffer amplifiers (Q192, Q272), then applied to the prescaler circuit (IC271). The prescaler circuit divides the applied signal, and outputs it to the VHF DDS circuit (IC131) via the buffer amplifier (Q271). The VHF DDS circuit generates digital signals using the applied signals as a clock frequency. The phase detector section in IC131 compares its phase with the reference frequency that is generated at the reference oscillator (X512). IC131 outputs off-phase components as pulse signals via pins 51, 52. The output pulses are converted into DC voltage at the loop filter circuit (IC161a) and then applied to the VHF VCO circuit. The D/A converter (R101–R124), low-pass filter (L101–L103, C103–C110) and buffer amplifier (IC101) circuits are connected to the DDS output to convert the digital oscillated signals into smooth analog signals. 4-3-2 UHF PLL CIRCUIT (PLL UNIT) The UHF PLL circuit generates the 1st LO frequency, and the signal is applied to the UHF 1st mixer circuit in the PA unit as the “B1LO” signal. The PLL circuit consists of a VCO, prescaler and DDS circuits. The signal generated at the UHF VCO circuit (Q391, D391–D394) is amplified at the buffer amplifiers (Q392, Q472), then applied to the prescaler circuit (IC471). The prescaler circuit divides the applied signal, and outputs it to the UHF DDS circuit (IC331) via the buffer amplifier (Q471). The D/A converter (R301–R324), low-pass filter (L301–L303, C103–C311) and buffer amplifier (IC301) circuits are connected to the DDS output to convert the digital oscillated signals into smooth analog signals. 4-2-9 APC CIRCUIT (MAIN UNIT) The APC (Automatic Power Control) circuit protects the power amplifiers on the PA unit from excessive current. Current drain of power amplifiers is detected by voltage drops at a resistor (PA unit; R305) between VCC and PAHV lines. The original voltage (ICH) and dropped voltage (ICL) are applied to the APC differential amplifier (MAIN unit; IC1601d). The signal output from the differential amplifier reduces IF amplifier gain until these voltages are well-balanced. 4-4 UX-910 (1200 MHz BAND UNIT) UX-910 is an optional 1200 MHz band unit for IC-910H. This unit covers 1240–1300 MHz frequency range. 4-4-1 ANTENNA SWITCHING CIRCUIT (for RX) Received signals from the antenna connector (CHASSIS; J501) are applied to the transmit/receive switching circuit (RL51). The transmit/receive switching circuit leads receive signal to the RF circuit while receiving. However, the circuit leads the transmit signal from the RF power amplifier to the antenna connector while transmitting. 4 - 5
Page 1 and 2: SERVICE MANUAL VHF/UHF ALL MODE TRA
Page 3 and 4: TABLE OF CONTENTS SECTION 1 SPECIFI
Page 5 and 6: ■ RECEIVER • Receive system : V
Page 7 and 8: • PA UNIT TX/RX switching relay (
Page 9 and 10: SECTION 3 DISASSEMBLY AND OPTION IN
Page 11 and 12: • UT-102 VOICE SYNTHESIZER UNIT q
Page 13 and 14: SECTION 4 CIRCUIT DESCRIPTION 4-1 R
Page 15: 4-1-11 NOISE BLANKER CIRCUIT (MAIN
Page 19 and 20: SECTION 5 ADJUSTMENT PROCEDURES 4-1
Page 21 and 22: • PLL AND MAIN UNITS R570 30.2 MH
Page 23 and 24: • PA UNIT 144M receiver peak/gain
Page 25 and 26: • PA UNIT 430M peak adjustment fo
Page 27 and 28: • PA UNIT P501 RF peak pre-settin
Page 29 and 30: • MAIN UNIT R202 Drive level adju
Page 31 and 32: SOFTWARE ADJUSTMENT (continued) ADJ
Page 37 and 38: CP321 Idling check point CP322 Idli
Page 39 and 40: R67 APC adjustment CP401 APC check
Page 41 and 42: [DISPLAY BOARD] REF ORDER NO. NO. D
Page 43 and 44: [RIT BOARD] REF ORDER NO. NO. R2 72
Page 45 and 46: [PLL UNIT] REF ORDER NO. NO. DESCRI
Page 47 and 48: [PLL UNIT] REF ORDER NO. NO. DESCRI
Page 49 and 50: [MAIN UNIT] REF NO. ORDER NO. DESCR
Page 53 and 54: [MAIN UNIT] REF ORDER NO. NO. DESCR
Page 57 and 58: [PA UNIT] REF NO. ORDER NO. DESCRIP
Page 59 and 60: [PA UNIT] REF ORDER NO. NO. DESCRIP
Page 65 and 66: [MAIN UNIT] — UX-910 REF NO. ORDE
Page 67 and 68:
[MAIN UNIT] — UX-910 REF ORDER NO
Page 69 and 70:
[MAIN UNIT] — UX-910 REF ORDER NO
Page 71 and 72:
[PA UNIT] REF. NO. ORDER NO. DESCRI
Page 73 and 74:
2SK2855 2SK2973 2SK2975 3SK131 T2 L
Page 75 and 76:
SECTION 9 9-1 VR-A BOARD • TOP VI
Page 77 and 78:
1-1-32, Kamiminami, Hirano-ku, Osak
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IC-910H Service manual - n7tgb

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